1. Field of the Invention
The present invention relates generally to devices and methods used in conjunction with external chest compression and decompression as a part of cardiopulmonary resuscitation procedures. In particular, the present invention relates to devices and methods for increasing cardiopulmonary circulation induced by chest compression and decompression when performing cardiopulmonary resuscitation.
Worldwide, sudden cardiac arrest is a major cause of death and is the result of a variety of circumstances, including heart disease and significant trauma. In the event of a cardiac arrest, several measures have been deemed to be essential in order to improve a patient's chance of survival. These measures must be taken as soon as possible to at least partially restore the patient's respiration and blood circulation. One common technique, developed approximately 30 years ago, is an external chest compression technique generally referred to as cardiopulmonary resuscitation (CPR). CPR techniques have remained largely unchanged over the past two decades.
With traditional CPR, pressure is applied to a patient's chest in order to increase intrathoracic pressure. An increase in intrathoracic pressure induces blood movement from the region of the heart and lungs towards the peripheral arteries. Such pressure partially restores the patient's circulation. Traditional CPR is performed by actively compressing the chest by direct application of an external pressure to the chest. After active compression, the chest is allowed to expand by its natural elasticity which causes expansion of the patient's chest wall. This expansion allows some blood to enter the cardiac chambers of the heart. The procedure as described, however, is insufficient to ventilate the patient. Consequently, conventional CPR also requires periodic ventilation of the patient. This is commonly accomplished by mouth-to-mouth technique or by using positive-pressure devices, such as a self-inflating bag which relies on squeezing an elastic bag to deliver air via a mask, endotracheal tube or other artificial airway.
In order to increase cardiopulmonary circulation induced by chest compression, a technique referred to as active compression-decompression (ACD) has been developed. According to ACD techniques, the active compression phase of traditional CPR is enhanced by pressing an applicator body against the patient's chest to compress the chest. Such an applicator body is able to distribute and apply force substantially evenly over a portion of the patient's chest. More importantly, however, the applicator body is sealed against the patient's chest so that it may be lifted to actively expand the patient's chest during the decompression step. The resultant negative intrathoracic pressure induces venous blood to flow into the heart and lungs from the peripheral venous vasculature of the patient.
Also of importance to the invention are ventilation sources that are used in connection with CPR techniques to properly ventilate the patient. One type of ventilation source is the AMBU bag available from AMBU International, Copenhagen, Denmark. The AMBU bag can also be used in connection with a positive end-expiratory pressure (PEEP) valve, available from AMBU International, to treat some patients with pulmonary and cardiac diseases. However, until the present invention, a positive end-expiratory pressure valve in connection with a ventilation source has not been used with any CPR techniques.
With both traditional CPR and ACD-CPR techniques, an increase in the amount of venous blood flowing into the heart and lungs from the peripheral venous vasculature would be desirable to increase the volume of oxygenated blood leaving the thorax during the subsequent compression phase. It would therefore be desirable to provide improved methods and apparatus for enhancing venous blood flow into the heart and lungs of a patient from the peripheral venous vasculature during both conventional CPR and ACD-CPR techniques. It would be particularly desirable to provide techniques which would enhance oxygenation and increase the total blood return to the chest during the decompression step of CPR and ACD-CPR, more particularly of ACD-CPR. This can be accomplished according to the present invention by augmentation of both negative and positive intrathoracic pressure, thereby amplifying the total intrathoracic pressure swing. An invention for providing this crucial improvement is described.
2. Description of the Background Art
ACD-CPR techniques are described in detail in Todd J. Cohen et al., Active Compression-Decompression Resuscitation: A Novel Method of Cardiopulmonary Resuscitation, American Heart Journal, Vol. 124, No. 5, pp. 1145-1150, November 1992; and Todd J. Cohen et al., Active Compression-Decompression: A New Method of Cardiopulmonary Resuscitation, The Journal of the American Medical Association, Vol. 267, No. 21, Jun. 3, 1992. These references are hereby incorporated by reference.
The use of a vacuum-type cup for actively compressing and decompressing a patient's chest during ACD-CPR is described in a brochure of AMBU InternationaL A/S, Copenhagen, Denmark, entitled Directions for Use of AMBU.RTM. CardioPump.TM., published in September 1992. The AMBU.RTM. CardioPump.TM. is also disclosed in European Patent Application No. 0 509 773 A1. These references are hereby incorporated by reference.